filters - What exactly is stored in the buffer array in the code below? Is it the values of x[n-k] or something else?

What exactly is stored in the buffer array in the FIR Filter code below? Is it the values of x[n-k] or something else?

float filter (float value){
    for (int i = ntaps-1; i>0; i--){
        buffer[i] = buffer[i-1];
    }
    buffer[0] = value;
    for (int i = 0; i        output += buffer[i]*h[i];
    }
    return ouput;
}

Answer

It stores the last $ntap$ samples of the input. So it's $x[n], x[n-1], ..., x[n-N+1]$